1. Field of the Invention
This invention relates to a process for producing a cyclic urea by reacting a diamine with phosgene, which cyclic urea is expressed by the formula (I) ##STR2## wherein R represents hydrogen atom or a lower alkyl group and R' represents dimethylene group, a lower alkyl group-substituted dimethylene group, trimethylene group, a lower alkyl group-substituted trimethylene group, tetramethylene group or a lower alkyl group-substituted tetramethylene group, but a case where R represents hydrogen atom and R' represents dimethylene group, a case where R represents hydrogen atom and R' represents a lower alkyl group-substituted dimethylene group and a case where R represents methyl group and R' represents dimethylene group are excluded.
Cyclic ureas of the formula (I) such as 2-imidazolidinones, tetrahydro-2(b 1H )-pyrimidines, hexahydro-2H-1,3-diazepin-2-ones, etc. are useful substances as non-protonic polar solvents and as an intermediate for pharmaceuticals, pesticides, etc. In particular, they are superior solvents for high-molecular compounds such as polyamides, polyvinyl chloride, polyvinyl alcohol, polystyrene, polyurethanes, phenol resins, etc. and also form complexes with many inorganic salts to dissolve therein and further are used as solvents for many organic reactions.
2. Description of the Prior Art
A process for obtaining 2-imidazolidinones by reacting diamines corresponding to 2-imidazolidinones of the above formula with phosgene has not yet been known, but a process for obtaining 1,3-dimethyl-2-imidazolidinone which is a similar compound to the above cyclic ureas of the formula (I), with a yield of 13% by reacting N,N'-dimethyl-1,2-ethanediamine with phosgene in toluene solvent has been known (J. Chem. Soc., 1947, page 315). However, the present inventors carried out the reaction of N,N'-dimethyl-1,2-propanediamine with phosgene in toluene solvent according to the above process, but the yield of 1,3,4-trimethyl-2-imidazolidinone belonging to the cyclic ureas of the formula (I) was less than 20%.
Further, as the process for producing the above tetrahydro-2(1H)-pyrimidinones, a process of reacting N,N'-dimethyl-1, 3-propanediamine with phosgene in toluene (J. Chem. Soc. page 315, 1947) and a process of reacting N,N'-bis (trimethylsilyl)-1,3-propanediamine with phosgene, followed by hydrolyzing the resulting tetrahydro-1,3-bis(trimethylsilyl)- 2(1H)-pyrimidinone (Chem. Ber. Vol. 93, page 2813, 1960) have been known.
However, as to the process of reacting N,N'-diamino-1,3propanediamine with phosgene in toluene, the present inventors followed the process, but the yield was less than 20%. Still further, according to the process of reacting N,N'-bis (trimethylsilyl)-1,3-propanediamine with phosgene, while the yield was 75%, it is necessary to obtain a silylating material so that the process is also not a process which can be carried out by directly reacting phosgene and also it is necessary to use an expensive silylating agent.
Further, as a process for producing the above-mentioned hexahydro-2H-1,3-diazepin-2-ones, a process of obtaining hexahydro-2H-1,3-diazepin-2-ones by directly reacting 1,4-butanediamines with phosgene has not yet been known, but as an indirect process, a process of reacting N,N'-bis(trimethylsilyl)-1,4-butanediamine with phosgene and then hydrolyzing the resulting hexahydro-1,3-bis(trimethylsilyl)-2H-1,3-diazepin-2-one (Chem. Ber. Vol. 93, page 2813, 1960) has been known.
However, according to this process, it is necessary to obtain the silylated compound of 1,4-butanediamine in advance using an expensive silylating agent, and also the yield of the reaction of the diamine with phosgene (such a reaction with phosgene will be hereinafter referred to as "phosgenation reaction") is as low as 60% ; hence the process has not been commercially satisfactory.